1. Field of the Invention
The present invention relates to a light-emitting device and an illuminator, and more particularly, it relates to a light-emitting device including a light-emitting diode and an illuminator employing this light-emitting device.
2. Description of the Background Art
A light-emitting diode mounted with a photonic crystal on its light-emitting surface to be capable of improving efficiency for extracting light emitted from the light-emitting diode is known in general. This type of light-emitting diode is disclosed in “Highly directive light sources using two-dimensional photonic crystal slabs”, Applied Physics Letters, December 2001, Vol. 79, No. 26, pp. 4280–4282 or “Strongly directional emission from AlGaAs/GaAs light-emitting diodes”, Applied Physics Letters, November 1990, Vol. 57, No. 22, pp. 2327–2329, for example.
FIG. 13 is a sectional view for illustrating the structure of a conventional light-emitting diode mounted with a photonic crystal on its light-emitting surface. The structure of the conventional light-emitting diode having the photonic crystal mounted on the light-emitting surface is now described with reference to FIG. 13.
In the conventional light-emitting diode having the photonic crystal mounted on the light-emitting surface, an n-type cladding layer 202 of n-type AlGaAs, an emission layer 203 of p-type GaAs and a p-type cladding layer 204 of p-type AlGaAs are successively stacked on an n-type GaAs substrate 201, as shown in FIG. 13. Thus, the light-emitting diode has a double heterostructure. Periodically arranged striped (elongated) corrugation having a prescribed width and a prescribed depth are formed on the upper surface of the p-type cladding layer 204. A metal layer 205 of Ag is formed on the upper surface of the p-type cladding layer 204 having the aforementioned corrugation.
In the conventional light-emitting diode, as hereinabove described, the upper surface of the p-type cladding layer 204 is formed with the periodically arranged striped corrugation having the prescribed width and the prescribed depth while the metal layer 205 is formed on the upper surface of the p-type cladding layer 204 having the corrugation, thereby forming a portion having a dielectric constant periodically modulated with respect to the in-plane direction of the p-type cladding layer 204 and the metal layer 205. Thus, the p-type cladding layer 204 can also function as a photonic crystal. Consequently, the light-emitting diode emits light perpendicularly to the light-emitting surface, and extraction efficiency for the emitted light can be improved.
However, the aforementioned conventional light-emitting diode having the photonic crystal mounted on the light-emitting surface emits the light perpendicularly to the light-emitting surface, and hence it is difficult to obtain diffused light suitable for indoor illumination or the like. Therefore, it is disadvantageously difficult to apply the conventional light-emitting diode having the photonic crystal mounted on the light-emitting surface to illumination.